The radar identified a region in an area called Tushka where water formed a lake after overflowing from the Nile. At its largest extent - shown in the right hand image - the lake would have covered an area of 68,200 square kilometres. The lake appeared around 250,000 years ago - during a period of wet climate when the region would have been covered in grasslands - and dried up 80,000 years ago (Geology, DOI 10.1130/G31320.1).

The extent of the lake explains how fossilised fish from the last interglacial period ended up at Bir Tarfawi, 400 km west of the Nile. The fossils occur at the same elevation at the ends of runoff channels north of Selima Oasis in Sudan. At 190m above sea level (shown left) a smaller basin may have contained the lake as it shrank. Acheulian hand axes dating from the middle Pleistocene were found here.

Evidence points to mega-lakes also exiting in Chad, Sudan and Libya. The positions of these ancient oases could help explain migratory patterns of early humans.

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